It’s a myth that sudden cardiac death often occurs during exercise, says cardiologist Dr. Andrew Krahn, a professor at the University of British Columbia.

He and his research team reviewed the Ontario coroners’ reports from 2008 and found 174 cases of presumed sudden death in people between the ages of two and 40.

Heart disease — a group of conditions affecting the heart’s structure and functions — was present in 126 cases, mainly men between the ages of 18 and 40. But in 78 percent of those cases, the heart disease had not been recognized when the person was alive.

In 72 percent of all 174 cases, the person died at home. In only 11 percent of the cases did people die while engaged in moderate or vigorous exercise. A further nine per cent of adults died while running, shoveling snow, dancing or having sex.

Of the deaths involving children and adolescents, 33 percent died during activities such as gym class, swimming, paintball.

“If you are a 17-year-old hockey player and you’re at a hockey game and collapse, you’re much more likely to get media attention,” says Krahn.

“But nobody calls (media) when you die at home…..And where do most people spend most of their time? At home and at work.”

“There are a lot of people who have this unrecognized risk. Nobody hears the thunder we just the lightning bolt, so we need to devise systems to try to detect this before it happens.”

Exercise does increase stress on the heart and can trigger a sudden cardiac arrest, but those who exercise regularly are at lower risk, so you’re better off hitting the gym, says Krahn.

Every year up to 40,000 Canadians dies of sudden cardiac arrest, with less than two percent of the fatalities occurring in people under the age of 40, who appear healthy.

Cardiac arrest occurs when the heart unexpectedly stops beating, whereas a heart attack is when blood supply to the heart is slowed or stopped because of a blockage.

The study offers a glimpse into how big a problem unrecognized heart disease is, and its tragic consequences, says medical student Caileigh Pilmer, lead author of the study. (The research team is currently reviewing five years of data from the office of the coroner involving deaths of children and adolescents.)

A nationwide screening program would be the best way to detect heart disease, but there’s no reliable and cheap way of screening people effectively, says Pilmer. She suggests greater attention be paid to possible warning signs, such as fainting, palpitations and chest pains.